Add --radius-full variable

The `rounded-full` classname doesn't match the pattern of the other radius classnames:
```
rounded-xl: border-radius: var(--radius-xl)
rounded-2xl: border-radius: var(--radius-2xl)
rounded-3xl: border-radius: var(--radius-3xl)
rounded-full: border-radius: calc(infinity * 1px)
```
This PR makes `var(--rounded-full)` available to use like all the others in the theme.css.

Author: keithburgie

packages/tailwindcss/theme.css

@@ -354,6 +354,7 @@
   --radius-2xl: 1rem;
   --radius-3xl: 1.5rem;
   --radius-4xl: 2rem;
+  --radius-full: calc(infinity * 1px)
 
   --shadow-2xs: 0 1px rgb(0 0 0 / 0.05);
   --shadow-xs: 0 1px 2px 0 rgb(0 0 0 / 0.05);